/*
 *  cat_nonblock.c - open a file and display its contents, but exit rather than
 *  wait for input.
 */
#include <errno.h>  /* for errno */
#include <fcntl.h>  /* for open */
#include <stdio.h>  /* standard I/O */
#include <stdlib.h> /* for exit */
#include <unistd.h> /* for read */

#define MAX_BYTES 1024 * 4

int main(int argc, char *argv[])
{
	int fd;			/* The file descriptor for the file to read */
	size_t bytes;		/* The number of bytes read */
	char buffer[MAX_BYTES]; /* The buffer for the bytes */

	/* Usage */
	if (argc != 2) {
		printf("Usage: %s <filename>\n", argv[0]);
		puts("Reads the content of a file, but doesn't wait for input");
		exit(-1);
	}

	/* Open the file for reading in non blocking mode */
	fd = open(argv[1], O_RDONLY | O_NONBLOCK);

	/* If open failed */
	if (fd == -1) {
		puts(errno == EAGAIN ? "Open would block" : "Open failed");
		exit(-1);
	}

	/* Read the file and output its contents */
	do {
		/* Read characters from the file */
		bytes = read(fd, buffer, MAX_BYTES);

		/* If there's an error, report it and die */
		if (bytes == -1) {
			if (errno == EAGAIN)
				puts("Normally I'd block, but you told me not to");
			else
				puts("Another read error");
			exit(-1);
		}

		/* Print the characters */
		if (bytes > 0) {
			for (int i = 0; i < bytes; i++)
				putchar(buffer[i]);
		}

		/* While there are no errors and the file isn't over */
	} while (bytes > 0);

	return 0;
}
